题目：
We are playing the Guess Game. The game is as follows:
I pick a number from 1 to n. You have to guess which number I picked.
Every time you guess wrong, I'll tell you whether the number is higher or lower.
You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):
-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it!
Example:
n = 10, I pick 6. Return 6.
链接：
https://leetcode.com/problems/guess-number-higher-or-lower/#/description
3/17/2017
果然是简单题，但是要注意返回值的意义。
1 /* The guess API is defined in the parent class GuessGame. 2 @param num, your guess 3 @return -1 if my number is lower, 1 if my number is higher, otherwise return 0 4 int guess(int num); */ 5 6 public class Solution extends GuessGame { 7 public int guessNumber(int n) { 8 int lo = 1, hi = n; 9 int mid; 10 int ret; 11 12 while (lo <= hi) { 13 mid = lo + (hi - lo) / 2; 14 ret = guess(mid); 15 if (ret == 0) return mid; 16 else if (ret > 0) { 17 lo = mid + 1; 18 } else { 19 hi = mid - 1; 20 } 21 } 22 return 0; 23 } 24 }
官方解答里有更多内容，包括ternary search，以及与binary search的比较
https://leetcode.com/articles/guess-number-higher-or-lower/